Corrosion inhibition



Patented June 23, .1953

2,643,178 oormosIoN INHIBITION Aaron Wachter and Nathan Stillman, Berkeley,

Calif., assignors to Shell Development Com- 0, Calif., a corporation of pa y, San Francisc Delaware No Drawing. Application April 19, 1946, Serial No. 663,608

Claims.

The present invention relates to the prevention of corrosion of metal surfaces which corrosion normally occurs in the presence of water vapor and/or aqueous condensates. More particularly, this invention pertains to novel compositions capable of inhibiting such metal corrosion by providing an atmosphere containing one or more novel vapor-phase inhibitors in the immediate vicinity of metal surfaces. A particularly preferred embodiment relating to packaging of "a metal element in such a manner that corrosion thereof by water vapor and/or aqueous condensates is prevented, is disclosed and claimed in our copending application Serial No. 668,015, filed May 7, 1946.

During storagahandling, transportation, operation, and distribution of objects having metalcontaining surfaces, such as tools, machines, moving metal parts, machined surfaces, sheets of metal, steel cans, tanks, metal containers, shellcases, fire-arms, bullet-cases, rocket-heads, metal tubes, pipes, and conduit-enclosures, it is often necessary to prevent metal corrosion caused by Water vapor contacting such metal surfaces. Metal articles or articles having metallic surfaces which are unprotected from corrosion or only partly protected by inadequate means, such as a partially pervious coating, often require suitable corrosion-inhibitors which prevent metal parts from corroding in the presence of water vapor, liquid water, or aqueouscondensates which may contain compounds or salts which ordinarily promote corrosion.

Partially enclosed or completely enclosed metal-containing objects are usually housed, packaged, enveloped or placed in a container under such conditionsor by means of such an enclosing material that moisture is either present at the outset or may enter through the container walls, thereby causing corrosion. For example, although various machined parts are usually packaged in waxed or oiled paper or mother materials which in fact are only partially impermeable to water vapor, it has been found necessary to also coat the metal surfaces with a protective coating of for example, oil, grease, or the like, in order to obtain a further degree of corrosion prevention. In many cases additional corrosion preventive means have been resorted to, e. g., the use, within the container or package of a dehydrating agent of the type of silica gel or alumina. Even when the container walls are absolutely impervious to gases or water vapor, corrosion of the metal parts will still occur because it is substantially impossible to avoid entry of water vapor at the time when said parts are being placed into a container.

It is, therefore, an object of the present invention to provide .novel methods and means for inhibiting corrosion of corrodible metals. It is another object of the present invention to provide corrosion inhibitors which prevent water corrosion of metal surfaces. A further object is to provide volatile corrosion inhibitors suitable for preventing water-corrosion of the surfaces of metals disposed in a closed space. A still further object is to provide volatile or vaporizable corrosion inhibitors which prevent or inhibit corrosion of metal parts in the presence of water vapor. Another object is to provide materials containing corrosion inhibitors which volatilize and prevent corrosion of metal parts, particularly whenin contact with water. It is also an object of this invention to provide vaporizable corrosion inhibitors, which, in the substantial vicinity of a metal, prevent corrosion of the surfaces of various corrodible metals. It is also an object of this invention to provide volatile corrosion inhibitors, and methods and means of applying same whereby at atmosphere containing said corrosion inhibitor vapors is provided so that corrosion of metal surfaces in contact therewith and water vapor is significantly reduced orprevented. It is also an object of this invention to provide a method for preventing corrosion of metal surfaces during storage, shipping, use, and the like. A primary object of the invention is to provide corrosion inhibitors and means of utilizing same whereby an atmosphere substantially saturated with corrosion inhibitor vapors is maintained around a, metal partnormally subject to corrosion when in the presence of air and moisture.

It has now been discovered that corrosion of metal surfaces in presence of water vapor and oxygen is preventedby contact with vapors of salts of organic bases and nitrous acid; more preferably such corrosion is prevented by an atmosphere containing vapors of primary amine nitrite salts or particularly ofsecondary amine nitrite salts wherein condensation of such an atmosphere forms a liquid having a pH of at least 6. Preferably, the vapors of the organic salt of nitrous acid should be at least in partwatersoluble, although the degree of water-solubility may be Very low.

Representative classes of organic bases which are suitable for preparing the salts used as vapor phase inhibitors according to the present invention, include: primary amines, secondary amines, tertiary amines, cyclic secondary amines of .the

type of piperidine, oxazines, morpholine, thiazolines, and pyrrolidines; and various nitrogenous bases such as urea, thiourea, hydrazones, hydroxylamines, amidines, and guanidine. In any of the above nuclei, alkyl, cycloalkyl, terpinyl, bornyl, aralkyl, benzylyphenyl, aryl, and various substituent groups or atomic radicals may be More specifically and preferably, organic nitrogen base salts of nitrous acid include the following nitritesalts of: I

1. Primary. amines, such as (a) primary amines in which the'amin group is attached. to a second-- aryor a tertiary aliphatic carbon atom as in the following structural formulasz'.

wherein R1, R2 and R are hydrocarbon radicals which are aliphatic, alicyclic, heterocyclic, aromatic, or alkylated cyclic radicals, and may, if desired, contain preferably not more than one olefinic double bond, or R1 and R2 are joined in the form of a cyClo-aliphatic or heterocyclicaliphatic ring radical R3; (1)) primary amines in which'the amine group is attached to an aralkyl group as in the following structural formula;

wherein R4 is an aromatic hydrocarbon radical,

preferably a phenyl or alkylated phenyl radical and n is an integer which is preferably 1 or 2; (0) primary aliphatic amines, such as methyl amine, which react with nitrous acid in the presence of an excess of the amine to give a primary amine nitrite salt, (as distinguished from aprimary aliphatic amine which reacts with nitrous acid to yield nitrogen, an alcohol, or other reaction products).

2. Secondary amines, such as secondary'amines in which the amine group is attached to an aliphatic carbon atom, preferably a secondary or tertiary carbon atom, as represented by the following structural formulas:

including 4 vapor phase corrosion inhibitors of the present invention include:

Primary amines: methylamine, isopropyl amine, Z-amino-butane, tertiary butyl amine, 2-amino-l-methyl-pentane, various amyl, hexyl, heptyl, octyl, and higher homologous primary amines wherein the amine groupis attached to a secondary or tertiary carbon atom; cyclopentyl amine, alkylated cyclcpentyl amines, cyclohexylamine, mono-methylcyclohexy1amines, dimethyl cyclohexylamines, trimethyl cyclohexylamincs, other alkylated cyclohexylamines, bornyl amine, fenchyl amine, cycloterpenyl amines, pinyl amine, be'nzylamine, betaphenylethylamine, alkylated benzylamines, tetrahydro betanaphthylarnine, allyl amine, beta-methyl allyl amine, beta-chloro allyl amine, and their homologs and analogs.

Secondary amines: dimethyl-, di-ethyl-, di-

-n-propyl'-, di-isopropy1- di-butyl-amines; various secondary amines derived from amyl, hexyl, heptyl, octyl, and higher homologous alkyl groups; methyl isobutyl amine, N-methyl N-tertiary-butyl amine, N-alkyl N-cyclohexyl amine,

N-alkyl N-bornyl amine, di-bornyl amine, N-e methyl N cycloterpenyl amine, 'N isopropyl N- ('1) -menthyl amine, N-alkyl N-benzyl amines and their homologs and analogs dicyclopentyl amine, dicyclohexyl amine, alkylated dicyclohexyl amines; diphenylamine, dibenzylamine, di- (beta phenyl ethyl) amine; piperidine, piperazine, alkylated piperidines or piperazines; 1,4'-alkylated and unalkylated oxazines such as morpholine and ZAAfi-tetramethyl tetrahydro-l,3- oxazine; alkylated-1,3-thiazolines such as (B infitetramethyl tetrahydro-3-thiazoline.

Secondary amine type derivatives of alkylene dia-inines, such as:

wherein Ri'and R3 may be like or different aliphatic, alicyclic aralkyl, alkarylalkyl, heterocyclic, terpenic radicals, and wherein R2 isjan alkylene radical. Ihese R1 and R3 radicals for instance, may be isopropyl, butyl, cyclohexyl, benzyl, and/or bornyl radicals. The R2 radical is preferably an ethylene or propylene radical.

Tertiary amines: trimethyl amine, triethylamine, tri-n-propylamine, tri-isopropylamine, tributylamine, higher homologous and isomeric trialkylamines, variously N-substituted tertiary amineshaving different organic radicals on the amino nitrogen atom, e. g., alkyl, alicyclic, bornyl, fenchyl, aralkyl, and like homologs and analogs; and tertiary amine type derivatives of alkylene diamines.

- Quaternary ammonium bases: tetramethyl and higher tetraalkyl ammonium bases; trimethyl benzyl-, trimethyl cyclohexyle, tributyl decyl ammonium bases; various quaternary N-substituted ammonium bases havingv various organic radicals (of the type described above) on the quaternary nitrogen atom; pyridinium and alkylated pyridinium 0r quinolinium quaternary ammonium bases having an alkyl, cycloalkyl, or aralkyl group on the quaternary nitrogen atom, including methyl, butyl, .cyclohexyl, benzyl groups and like homologs-or analogs.

The various hydrocarbon radicals or groups of the above amines may also contain stable and inert polar substituent atoms orradicals, such as, chlorine, ether, thio-ether, alcohol, free amino, or nitro groups. Neutral ketone, ester and nitrile groups and aliphatic unsaturation may. also be present, particularly in the case of allyl and chlorallyl groups.

The salts of nitrous acid and the organic nitrogen bases described above, may usually be prepared by a stoichiometric reaction of an organic nitrogen base with nitrous acid.

Table I below sets forth representative organic nitrogen base nitrites as well as their respective Vapor pressures.

of the above compounds, di-isopropylamine nitrite, Z-aminc butane nitrite and morpholine nitrite are particularly suitable for the purposes of the present invention because of their relatively high vapor pressures, their relatively higher solubility in water, and in view of the fact that a higher vapor pressure of the inhibitor results in a more rapid distribution of its vapors throughout the contiguous atmosphere.

It will be appreciated that the amount of vapor phase inhibitor required varies depending on a number of variables, e. g., the severity of conditions under which it is to be employed, the particular vapor phase inhibitor used and the mode in which it is applied. Ingeneral, the placing of a sheet of paper or of an absorbent material impregnated with or coated by a minor amount of a vapor phase inhibitor (of the defined class) in the proximity of the metal enclosed in a package or other housing or enclosure means, pro vides satisfactory corrosion inhibition when between about 0.1 gm. to about 5.0 gm., and preferably approximately 1.0 gm. of the inhibitor is present per square foot of the inner container surface. Particularly satisfactory results are at tained when the inhibitor is present in such an amount as to allow between about 1 gm. and about 15 gm. (for average conditions about 6 gm.) thereof for each cubic foot of enclosed vapor space.

Stability of the present vapor phase inhibitors, and particularly the stability of organic nitrogen base nitrite salts, is adversely aifected by an environment which on contact with or dispersion in water, yields a solution having a pH value of less than approximately 6. In some instances the stability is also adversely affected by elevated temperatures, such as 120 F. or 150 F. Such and like factors which may render an organic nitrite salt unstable, are greatly lessened or entirely obviated by introducing an alkaline agent either into the inhibitor per se, or into the vapor space containing the vapors of the inhibitor. This addition of the. alkaline agent to the unvolatilized portion of the vapor phase inhibitor is particularly applicable in cases where the inhibitor has a tendency to decompose. Suitable stabilizing agents include organic or inorganic compounds which, dispersed in water, have a pH in excess of approximately 7. Suitable stabilizing agents include alkaline materials having dissociation constants greater than, approximately equal to or slightly less than the dissociation constant of the alkaline material which was combined to form the nitrite salt which it is desired to stabilize. Various alkaline stabilizing agents which were found to be particularly effecting were: di-isopropyl amine, dicyclohexyl amine, aliphatic primary amines containing from 16 to 18 carbon atoms, various high molecular weight amines, triethanol amine, di-isopropyl ammonium bicarbonate, dicyclohexyl ammonium bicarbonate, sodium carbonate, sodium chromate, sodium phosphate, isopropyl urea, diphenyl amine, or piperazine.

The particular stabilizing agent, and the optimum quantity thereof required to be effective depends'on a number of variables. between about 0.1% and about 25% of the stabilizer (by weight of the vapor phase inhibitor) are effective. It will be seen from the above that many alkaline materials have been found to be effective in stabilizing a salt of an organic nitrogen base with nitrous acid. In this respect any organic or inorganic compound which is capable of removing acidity or maintaining a pH value above about 6 is suitable as the stabilizing agent.

The vapors of amine nitrite salts may contain, and in a number of cases have been found to contain, vapors of the corresponding nitrosamine. In studies on stability it was found that the decomposition of some secondary amine nitrite salts was of an autocatalytic type. Decomposition of such an amine nitrite was also accelerated by small amounts of water. Such decomposition as a whole, however, was readily prevented by the presence of an alkaline agent of the class defined above.

It was stated above that an amine nitrite salt may be in equilibrium with the corresponding nitrosamine and water which are formed from the nitrite, and that the shift of the equilibrium.

wherein R represents an organic radical. According to the usual laws of equilibrium, an excess of either water or nitrosamine or both above the chemically equivalent amounts indicated in the above equation tends to force the equilibrium toward increasing the concentration of the amine nitrite. The presence of the nitrosamine is not detrimental to vapor phase corrosion inhibition; in fact, vapors of the nitrosamine itself were found to inhibit corrosion of metal where in the presence of water vapor. However, in a number of cases, they did not appear as effective as vapors of the corresponding amine nitrite salts when the latter were substantially free of nitrosamine.

The present vapor phase inhibitors comprising salts of organic nitrogen bases with nitrous acid can be applied either separately or in various mixtures of members of this class, or with other vapor phase inhibitors. In certain cases it is advantageous to apply a mixture of inhibitors containing an inhibitor with a relatively high vapor pressure and an inhibitor with a relatively low vapor pressure. In this way the highly volatile inhibitor more rapidly protects metals in its vicinity, whereas the less volatile inhibitor gradually builds up an atmosphere saturated with its vapor. The latter is either substantial- In" general,

1y not lost or only lost to a slight degree due to partial permeability of an enclosure, whereas the highly volatile inhibitor may escapefrom an enclosure to a relatively greater degree than the inhibitor having a lower volatility. Once initial rapid inhibition of corrosion'by the highly'volatile inhibitor has been provided, usually the best overall long-term inhibition is provided by an atmosphere sufficiently concentrated with an inhibitor having a relatively lower volatility, such as dicyclohexyl ammonium nitrite.

Vapor phase inhibition can also be obtained by preparing or forming a suitable inhibitor in situ. For example, a mixture of an acid nitrate and a reducing agent such as arsenic tri-oxide may be slowly reacted to yield nitrous acid-vapors in the presence of a volatile" organic amine, to form a volatile organic nitrogen base nitrite salt-the vapors of which may be allowed to fill the space enclosing the metal parts to corrosion. I I

Factors which are deemedto be important to obtain optimum corrosion inhibitionaccording to the present inventionare: The vapor phase inhibitor preferably should have a vapor pressure in excess of approximately- 0.00002 mm. Hg at 21 C. Better results are obtainable with a vapor phase inhibitor having a vapor pressure greater than about 000001 mm. Hg at 21 C. More rapid inhibition of corrosion is obtainable with a vapor phase inhibitor havinga vaporpressure greater than about 0.001 mm. Hg. at 21 c. Y

The vapor phase inhibitors preferably should P p ot ste a ins The vapor phase inhibitors should'preferably either be sufficiently stable at the temperatures of their normal usage, such as temperatures ranging from atmospheric temperature. to about 150 R, or the inhibitors should respondto stabilization by an alkalineagent or other means, as described hereinbefore.

The vapor phase inhibitors of the present invention, whether as such or disposed on or in inert substances, upon contact with, or dispersion in water, should'yield a solution having ;a pH of at least 6. Alkaline agents, either volatileor non-volatile may be used with the present inhibitors to maintain the desired pH.

The vapors of organic nitrogensalts of nitrous acid are more effective in preventing aqueous corrosion of various ferrous metals, e. g. steels, as well as couples of steels with zinc or copper or other metals, and aluminum and alloys of these metals. Satisfactory inhibition of corrosion of copper, and copper alloys, such as brass and bronze, is obtained when small amounts of volatile carbonates, such as ammonium carbonate or an organic nitrogen base carbonate, for example di-isopropyl ammonium bicarbonate or dicyclohexyl ammonium bicarbonate, are present in the 8. herein. Within any enclosure means, corrosion of metal surfaces by 'moisture'is prevented by enclosing, or making available therein, a vapor phase inhibitor. The latter can be originally introduced as a solid, a liquid, or a vapor, or-in solution, as an emulsion or dispersion, etc., as long as the inhibitor may vaporize and thus be present in the atmosphere around the metal. In the alternative, the inhibitor may be introduced as a vapor. In the case of enclosed metal articles, the inhibitor may be disposed as crystals or as a powder in various porous containers; or the metal article or the wrapping material. thereof may be coated with material containing the vapor phase inhibitor. In one of the preferred embodiments of the invention, it was found advantageous to use wrapping material, such as paper, which was first impregnated with the vapor phase inhibitor. In another embodiment, waxed paper was warmed to melt. or soften the surface layer on one side thereof, andcrystals or powdered diisopropyl ammonium nitrite, or the like, was then sprinkled upon the partially melted wax. The latter was cooled, and excess vapor phase inhibitor was shaken oiT. The resulting waxed paper coated with the-vapor phase inhibitor was found to be an effective supplier of corrosioninhibiting vapors. Absorbent materials such as cotton, wool, cloth, silica gel, alum na gel, fullers earth, paper, and activated carbon are some examples of materials which can be impregnated with the above vapor phase inhibitors. In cases wherein free circulation of air is prevented. around metal articles in storage, the present inhibitors are eiiectively applied by introducing them as vapor, or by providing an atmosphere containing inhibitor vapor around such metal articles. Corrosion by circulation of air over metal surfaces'can be prevented by substantially saturating the introduced air with vapors of the present inhibitors. Metal parts can also be coated with the vapor phase inhibitor by depositing the latter from a solution or a dispersion, or from heated vapors contacting a metal, or by incorporating the inhibitor in relatively non-volatile coating materials.

The following are other techniques of applying the vapor phase inhibitors:

' The metal walls or parts enclosed within machinery or instruments are prevented from corroding by either enclosing or making available the present vapor phase inhibitors within the vapor spaces present and enclosed by such metal articles or mechanisms, e. g., as in hydraulic mechanisms,

gyroscopic stabilizers, or bomb sight mechanisms. Ina preferred method the vapor phase inhibitor is simply disposed in and allowed to vaporize from a hydraulic fluid introduced into such mechanisms. When disposed in a fluid, the vapor phase inhibitor present in' the liquid phase inhibited corrosion of metals contacting this liquid, and also inhibited corrosion in the vapor phase above such fluid. The corrosion of the combustion zone'and adjacent surfaces of internal combustion engines may be prevented by connecting inlets thereto with sources capable of supplying the vapor phase inhibitor.

Aerosols are also effective for distributing the present vapor phase inhibitors. In such a case, the inhibitor is dissolved in a liquefied, normally gaseous solvent which is under sufficient pressure in a vessel to maintain the solvent in its liquid state, The solution of the inhibitor thus prepared is released through an orifice in the vessel, and as a result, the inhibitor is distributed gases which do not react with a chosen inhibitor,

can be used in preparing these aerosols.

It has been additionally found that the present inhibitors are antiwear agents and reduce the corrosive wear of moving engine parts in, for

example, automotive engines, aircraft engines, and other internal combustion engines.

Therefore, the present vapor phase inhibitors may be incorporated into lubricating oils, thereby reducing wear of the lubricated metal parts while at the same time inhibiting corrosion.

' For purposes of further illustration, reference will now be made to the following examples, it being understood that there is no intention of being limited to the specific conditions disclosed therein. Example I Seven steel bolts, each of which was {*5 inch in diameter and 3 inches long, were solvent washed, electrolytically cleaned, and the threaded These corks were then' ends inserted into corks. used as stoppers for 2-ounce bottles. In this way the bolts were suspended in the vapor space of these bottles. Six of the bolts were suspended in bottles each of which contained 0.2 ml. of dis tilled water and 0.2 gm. of a vapor phase inhibitor. The bottle containing the seventh bolt was provided with 0.2 ml. of distilled water only. The

bolts were not'in contact with the walls, bottom or liquids contained in the sample bottles. The

vapor phase inhibitors thus tested in the respective bottles were: di-isopropylamine nitrite, morpholine nitrite, cyclohexylamine nitrite, piperidine nitrite, dibenzylamine nitrite, dicyclohexylamine nitrite. For a period of 14 days all of the bottles were subjected to alternate heating and cooling cycles, each bottle being heated to C. for a period of 10 minutes, followed by cooling to 0 C. for 10 minutes and then permitted to stand at room temperature. Three such cycles were carried out during each day of the test.

At the end of this 14-day test period, examination of all of the seven bolt specimens showed that only the seventh specimen (which had not-been subjected to the vapors of one of the amine nitrites), was badly rusted. The test with the sixth specimen in which dicyclohexyl amine nitrite was used, showed over 90% protection (prevention of rusting) as compared to the control experiment. The tests with the other live specimens showed complete preventio n of rusting due to the presence of the respective mentioned vapor phase inhibitors. Other tests showed that dicyclohexylamine nitrite also was 100% effective as a vapor phase inhibitor in preventing corrosion of steel.

Emample II Two steel-bolt specimens were given the same preparatory treatments and then tested by means of suspension in sample bottles in the same man- 7 ner as described above for Example I, except for the following diiferences: In the bottom of each sample bottle there was placed afolded pad of kraft paper, in each instance amounting to 8 square inches of the paper. In one of the-bottles, the kraft paper had absorbed therein 01 gm. of di-isopropylamine nitrite and 0.1 ml. ofdistilled water. In the other bottle the paper had absorbed therein only 0.1 ml. of distilled water specimens.

10 (without any vapor phase inhibitor being present). These two specimens were suspended in the respective bottles, stoppered tightly, and subjected to the alternate heating and cooling cycles described in Example .I for a period of 37 days. At the end of this test period, it was found that the specimen disposed in the bottle containing the Vapor phase inhibitor was preserved in its original appearance.

Example III Two steel bolt specimens were prepared by solvent washing, followed by wire brushing and then screwed into the fitting nut just far enough that the latter acted as a supporting base in which the bolt stood in a vertical position. Each of the prepared bolts was placed upright upon the respective bottom of each of two 2-ounce sample bottles. In a prepared recess in the cork of the bottle containing the first of these specimens there was. placed a small piece of cotton which had absorbed thereon 0.2 ml. of distilled water and 0.1 gm. of morpholine nitrite. The same amount of distilled water but without any vapor phase inhibitor, was absorbed in the same manner on a piece of cotton inserted into a prepared recess of the cork of the other of the two bottles. The respective bolts were not in contact with the cotton orthe materials absorbed in the cotton. Thees corked bottles were allowed to stand at normal room temperature for a period of 76 days. At the end of this test period, the steel specimen which was subjected to the action of morpholine nitrite vapors was free from rust. The surface of this steel specimen was shiny as it had been at the start of the test. On the other hand, the other steel specimen was so severely rusted that the surface of it had a rusty appearance and had lost its original shiny polished surface.

Example IV Two inch low-carbon steel plates were machined to a inch by 3 inches strip and wire .brushed to a bright metallic sheen. An inner wrap of neutral kraft paper and an outer wrap of laminatedmetal foil paper provided with an internal coating of a thermoplastic resin was provided around one of the described steel-plate The outer laminated metal foil wrap was heat sealed. The other steel plate was packaged in the identical manner except that the inner wrap of the neutral kraft paper, which in eachinstance measured 2 inches by 4 inches, was impregnated by dipping it in a 50% (by weight) aqueoussolution of' morpholine nitrite. After dipping, the paper was dried by suspension for about 10 minutes in an air blast maintained at approximately 50 C. After such drying, the kraft paper contained approximately 0.1 gm. of the inhibitor. 1 f

' "Both specimens,- after packaging, were iminerse'd in synthetic sea water prepared accord;- ing toU. S. Bureau of Ships specification 14-0-15 (INT) (1943) ,for a period of 26 days, the water being maintained at a temperature of approximately 30 C. during the test. At the end of the test period these packages were opened. It was discovered that the steel plate wrapped in paper which did not contain 'any amine nitrite was badly corroded with rust. On'the other hand,

V 11 7 V the steel plate packaged with the amine nitrite in the inner wrap retained its original polished and unblemished condition and appearance.

Example V V A test similar to that described in connection with Example II was made with ah assortment proximately es inch in diameter was punched in the cellulose acetate windowof each box in order to allow ample breathing. These two boxes were alternately chilled to C. and warmed to 30 (-3. several timesa day {or six Weeks. After this period of time it was found that considerable rust was evident on the steel parts in the box containing the untreated li raft paper liner, but that there was no rust on the steel parts in the box lined with the paper containing the di-isoprowl-am ium n Example VI Vapor phase corrosiontests were made with di isopropy1ar'nmonium nitrite to determine the effects on specimens of SA. E. 1020 steel and 24; ST aluminum in coupled combination and also on the S. A. E. 1020 steelattached to a steel bolt. A one-half by one inch specimen or the metal alloy, coupled by a steel bolt through holes in each metal sample, was suspended in the vapor space of an 8 oz. wide-mouth bottle by meansof a wire hook in a parafiined cork stopper of the bottle. A 16 sq. inch piece oi kraft paper impregnated with approximately 0.2 gm. of diisopropylammonium nitrite, was placed on the bottom of a bottle of one series 'to be tested, while duplicate bottles containing the metals for control experiments were prepared containing "the same amount of untreated kraft paper. To each of the containers was added 0.2 ml. of distilled water. All of the bottles were maintained at 30 (3. for 73 days, after which time the specimens were removed, uncoupled, inspected and the weight loss determined after removal of any corrosion product, when present. It was found that, in the cases where di-isopropylammonium nitrite was used, there was no corro'sionjo'n either metal on the aluminum couple, and no corrosion (rust) on the 1-020 steel. On the otherhand, in the control experiment (in which no di-isopropylammonium-nitrite was used) there was bad and uniform rusting of the steel and some corrosion of the aluminum on the S. A. E. 1020 steel-24'ST' aluminum couple, and fine rustv specks over the entire surface of the steel.

Er'a'mple VII A by 3 inch specimen of aluminum was wrapped in 2 by 4 inch pieces of kraft paper impregnated with di-isopropylammonium nitrite which was then placed in another envelope made by folding 5 by 5 inch pieces of grade A paper; the last envelope was then sealed with apressuresensitive, waterproof tape. Another aluminum specimen was similarly prepared, the only difference being that it was wrapped in an untreated piece of the said kraft paper. The envelopes or packages. thus produced were suspended over water at 30 C. for 2 months, whereupon it was a'ciaiis 12 found that, whereas the, aluminum specimen wrapped in'the paper treated with di-isopropylammonium nitrite wasnot corroded, the aluminum specimen wrapped in the untreated paper had considerable white corrosion.

I Example VIII A number of tests were effected: In each case a low-carbon steel specimen, /2 inch by 2 inches, was first cleaned electrolytically, neutralized with sodium carbonate, rinsed in distilled water, and then dried by carefully rinsing with acetone and. drying. The steel specimenwas then weighed andsuspended'inthevapor space of a l25-ml. bottle by means ofa glass hook placed ina c'ork fitted into the under side of a hollow stopper. One-half gram of the compound to be tested and 0.5 ml. of distilled water were placed at the bottom of eachbottleimaintained in the upright position) and then the stopper with the attached steel specimen was put into place. This stopper was sealed with a silicone stopcock grease. The time-prepared bottle and contents were maintained at 150 F. for 7 days, after which the specimens were removed, washed with acetone, dried in a vacuum dessieator, and the weight changes determined The following results were obtained:

' Approximate Pm- .Gam Inhibitor Weight ff g swim (in GU15.) rea gainst Rustin x None .0579 5% protection.

o .1022 Dl-Spoondary-butylammonlum n'i- 0026 protection.

trl e. Di-cyclohexylamr'nonium nitrite. .0101 90% protection. -Di-Isopropylammonium nitrite.. .0052 90% protection.

Dq. .0163 Do. Guanidinium 'N itrit'e 0008 Do.

' Exam le IX An i i inch by 2 inch low-carbon steel specimen was'suspended from a clean cork into a 4-02. bottle above a mixture of one gram of piperazonium nitrite and one ml. of distilled water. Another steel sample was likewise suspended in a bottle containing only the water; The steel samples were first cleaned with a wire brush, then washed with acetone and dried. The stoppered bottles containing the samples were heated or maintained at 50 C. with the exception that once or twice 'each day they were chilled to -12 C. for one hour. The control sample demonstrated that rusting occurred less than one hour after starting of the initial heating. On the other hand, the vapors of piperazonium nitrite completely prevented the steel from any noticeable rusting during 24 hours of operation.

i -Ema'mpleX A test was run as in Example IX, except that trimethyl ammonium 'nit'rite'was used as the inhibito'r. It was found that "trimethyl'ammonium nitrite was a satisfactory vapor phase inhibitor: the metal specimen (which was tested for a'total of 23 hours at 50 C. and 49 hours at room temper-attire (about 25C.) showed marked inhibition or rusting. On the other hand, the control sample (treated in the same manner but in the absence of the inhibitor) was completely covered with rust.

The term hydrocarbyl is used herein in accordance with the definition in 'Degering, Out.- line of Qrganic lxlitrogen Con- -pounds,f University Lithoprinters, Ypsilanti, Michigan (1943), page '13 59, namely, to designate a radical obtained by the loss of a hydrogen atom from any hydrocarbon.

The present application is a continuation-inpart of the copending application Serial No. 557,358, filed October 5, 1944, now abandoned.

We claim as our invention:

1. In a method for inhibiting corrosion of a metal normally corrodible by contact with water vapor and oxygen, the steps of disposing said metal in an enclosed space, and disposing,"in said space, an amount suficient to produce a corrosion-inhibiting concentration of vapors thereof of dicyclohexyl amine nitrite.

2. In a method for inhibiting corrosion of a metal normally corrodible by contact with water vapor and oxygen, the step of maintaining, in'

the immediate presence of said metal, an atmosphere containing a corrosion-inhibiting concentration of vapors of dicyclohexyl amine nitrite, said atmosphere, upon dispersion in water, yielding a solution having a pH value of at least 6.

3. In a method for inhibiting corrosion of a metal normally corrodible by contact with water vapor and oxygen, the step of forming, in the immediately vicinity of said metal, and subjecting said metal to, an atmosphere containing a corrosion-inhibiting concentration of vapors of V dicyclohexyl amine nitrite, said atmosphere upon dispersion in water, yielding a solution having a pH value of at least 6.

4. In a method for inhibiting corrosion of a metal normally corrodible by contact with water vapor and oxygen, the steps of disposing said metal in an enclosed space, and disposing, in said space, an amount sufficient to produce a corrosion-inhibiting concentration of vapors thereof of diisopropyl amine nitrite.

5. In a method for inhibiting corrosion of a metal normally corrodible by contact with Water vapor and oxygen, the step of maintaining, in the immediate presence of said metal, and subjecting said metal to, an atmosphere containing a corrosion-inhibiting concentration of vapors of diisopropyl amine nitrite, said atmosphere, upon dispersion in water, yielding a solution having a pH value of at least 6.

6. In a method for inhibiting corrosion of a metal normally corrodible by contact with water vapor and oxygen, the step of forming, in the immediate vicinity of said metal, and subjecting said metal to, an atmosphere containing a corrosioninhibiting concentration of vapors of diisopropyl amine nitrite, said atmosphere upon dispersion in water, yielding a solution having a pH value of at least 6.

'7. In a method for inhibiting corrosion of a metal normally corrodible by contact with water vapor and oxygen, the step of forming, in the immediate vicinity of said metal, and subjecting said metal to, an atmosphere containing a corrosion-inhibiting concentration of vapors of a dialkyl amine nitrite, said nitrite salt having a vapor pressure of at least 0.0001 mm. Hg. at 21 C., said atmosphere, upon dispersion in water, yielding a solution having a pH value of at least 6.

8. In a method for inhibiting corrosion of a metal normally corrodible by contact with water vapor and oxygen, the step of forming, in the immediate vicinity of said metal, and subjecting said metal to, an atmosphere containing a corrosion-inhibiting concentration of vapors of a N-dicycloalkyl amine nitrite having a vapor pressure of at least 0.0001 mm. Hg. at 21 C., said atmosphere upon dispersion in water, yielding a solution having a pH value of at least 6.

9. In a method for inhibiting corrosion of a metal normally corrodible by contact with water vapor and oxygen, the step of forming, in the immediate vicinity of said metal, and subjecting said metal'to, an atmosphere containing a corrosioninhibiting concentration of vapors of a secondary amine nitrite having a vaporpressure of at least 0.0001 mm. of Hg. at 21 C., said atmosphere, upon dispersion in water, yielding a solution having a pH value of at least 6.

10. In a method for inhibiting corrosion of a metal normally corrodible by contact with water vapor and oxygen, the step of forming, in the immediate vicinity of said metal, and subjecting said metal to, an atmosphere containinga corrosioninhibiting concentration of vapors of an organic nitrogen-base nitrite salt having a vapor pressure of at least 0.00002 mm. Hg. at 21 C., said atmosphere, upon dispersion in water, yielding a solution having a pH value of at least 6.

11. In a method for inhibiting corrosion of a metal normally corrodible by contact with water vapor and oxygen, the step of forming, in the immediate vicinity of said metal and subjecting said metal to, an atmosphere containing a corrosioninhibiting concentration of an organic ammonium nitrite salt having a vapor pressure of at least 0.00002 mm. Hg. at 21 C., said atmosphere. upon dispersion in water, yielding a solution having a pH value of at least 6.

12. In a method for inhibiting corrosion of a metal normally corrodible by contact with water vapor and oxygen, the step of forming in the immediate vicinity of said metal and subjecting said metal to an atmosphere containing a corrosioninhibiting concentration of a nitrite salt of an unsubstituted N-hydrocarbyl amine, said salt having a vapor pressure of at least 0.00002 mm. H at 21 C., said atmosphere, upon dispersion in water, yielding a solution having a pH value of at least 6.

13. In a method for inhibiting corrosion of a metal normally corrodible by contact with water vapor and oxygen the steps of disposing of said metal in an enclosed space and disposing in said space an amount sufficient to produce a corrosioninhibiting concentration of vapors of an organic nitrogen base nitrite salt having a vapor pressure of at least 0.00002 mm. Hg. at 21 C., said atmosphere, upon dispersion in water, yielding a solution having a DH value of at least 6.

14. In a method for inhibiting corrosion of a metal normally corrodible by contact with water vapor and oxygen the steps of disposing said metal in an enclosed space and disposing in said space an amount suiiicient to produce a corrosion-inhibiting concentration of vapors of a secondary amine nitrite salt having a vapor pressure of at least 0.00002 mm. Hg. at 21 C., said atmosphere, upon dispersion in water, yielding a solution having a pH value of at least 6.

15. In a method for inhibiting corrosion of a metal normally corrodible by contact with water vapor and oxygen, the step of maintaining in the immediate presence of said metal, an atmosphere containing a corrosion inhibiting concentration of an N -dicycloalkyl ammonium nitrite having a vapor pressure of at least 0.0001 mm. Hg. at 21 C., said atmosphere upon dispersion in water yielding a solution having a pH value of at least 6.

AARON WACHTER. NATHAN STILLMAN.

(References on following page) Rafe t a n m file of 1; m: Number Name Date names f e 1 6 his pate 2,416,734 Boggs et a1. Mar. 4, 1947 UNITED STATES PATENTS 2,419,327 Wachter Apr. 22, 1947 Number Name Date 5 33 2 Wachtel: 7 3 2,148,862 Kern 2 939 2:3 0 Wachtel 16, 1 4

2,239,841 Cook Apr. 29, 1941 4 2,304,950 Parker etal Dec. 15, 1942 OTHER REEERENCES 2 3 3 3 9 Br'jggmann Jul 6, 1943 Ex parte Appeal Number 5286, April 4, 1947 Smith Sept, 5, 194 10 C se No. 213.) 29 J. P. o. s. 456. 

11. IN A METHOD OF INHIBITING CORROSION OF A METAL NORMALLY CORRODIBLE BY CONTACT WITH WATER VAPOR AND OXYGEN, THE STEP OF FORMNG, IN THE IMMEDIATE VICINITY OF SAID METAL AND SUBJECTING SAID METAL TO, AN ATMOSPHERE CONTAINING A CORROSIONINHIBITING CONCENTRATION OF AN ORGANIC AMMONIUM NITRITE SALT HAVING A VAPOR PRESSURE OF AT LEAST 0.00002 MM. HG. AT 21* C., SAID ATMOSPHERE, UPON DISPERSION IN WATER, YIELDING A SOLUTION HAVING A PH VALUE OF AT LEAST
 6. 